Currently, in the field of shoe manufacture, shoes are known which are provided with an upper assembly which comprises a membrane that is impermeable to water in the liquid state and permeable to water vapor.
Such shoes are generally appreciated because they combine the waterproofing provided by a waterproof sole with the waterproofing of the upper assembly, yet allowing vapor permeation of the foot through the upper assembly.
Membranes currently commonly used are made of expanded polytetrafluoroethylene, e-PTFE, or polyurethane, PU, and have an extremely limited tensile strength and therefore in order to protect their integrity substantially they cannot be shaped by elastoplastic deformation so as to adapt to the curves and cambers that the upper assembly has in order to adapt to the shape of the shoe.
In particular, at the rim of the upper assembly that is turned over so as to lie in the plantar region of the shoe in order to be joined to the insole, the upper assembly easily forms wrinkles and corrugations particularly at the more curved regions, for example at the heel and at the toe.
These wrinkles and corrugations, of the membrane as well, make difficult an effective grip on the membrane by material adapted to seal it to the sole, or optionally to a further membrane provided in the bottom of the shoe.
Nowadays, therefore, the need is strongly felt to devise increasingly simple and effective solutions for sealing the waterproof sole to the membrane of the upper assembly.
A solution currently devised consists in providing a band made of a net that is permeable to sealing material which is stitched to the upper, so as to replace its lower edge, and during use faces the edge of the inner lining that lines the upper internally, forming the upper assembly with said upper.
The waterproof membrane, which is gripped by sealing material that permeates the net band and also grips the sole or constitutes the material thereof by means of which the sole is formed by molding directly on the upper assembly stitched to the insole, is integrated in the multilayer inner lining.
U.S. Pat. No. 7,127,833 teaches to provide said band by using net which is substantially extensible, optionally elastically, in order to adapt to the curvature of the shape of the shoe in the joining regions between the insole and the upper assembly, where it connects the upper to the insole, and thus limit or avoid the formation of wrinkles and corrugations.
A drawback of a shoe provided according to the teaching of said patent consists in that water can penetrate through the upper and stagnates between said upper and the membrane integrated in the lining.
In order to avoid this drawback, patent WO2008119683 teaches to provide an upper that is joined directly to a membrane that is impermeable to water and permeable to water vapor.
However, the greater thickness of the materials generally used to provide the upper and their greater rigidity easily induce the formation of corrugations and wrinkles that are more substantial than those of the edge of the lining correspondingly in their region for joining to the insole.
This makes it even more difficult to solve the problem of achieving an effective grip to the membrane of sealing material that allows to obtain a shoe that is waterproof also at the connection of its upper assembly to its bottom.
Moreover, this problem is worsened when it is combined with the need to achieve an effective sealing of the membrane of the upper to a second membrane provided in the lower part of the shoe, therefore in the bottom or in the insole.
This second membrane, which is impermeable to water and permeable to water vapor, is adapted to close in a waterproof and vapor-permeable manner holes or openings provided through the bottom of the shoe in order to allow easy vapor permeation of the sole of the user's foot.
To make it also waterproof, a shoe that is vapor-permeable both at the sole and at the upper must have an effective waterproof seal between the membrane of the upper and the second membrane.